<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="../js/vue.js"></script>
</head>

<body>
    <div id="demo">
        <p>天气： {{weather}}</p>
        <button @click="isHot=!isHot">变天</button>
    </div>
    <script>
        Vue.config.productionTip = false
        new Vue({
            el: '#demo',
            data: {
                isHot:true,
                weather:'炎热'
            },
            watch:{
                // isHot:{
                //     handler(value){
                //         this.weather = this.isHot ? '炎热' : '凉爽'
                //     }
                // }

                /**
                 *  当业务不需要 deep  immediate 时，可以直接简写成一个函数
                 */
                isHot(value,oldValue){
                    console.log(value, oldValue)
                    this.weather = this.isHot ? '炎热' : '凉爽'
                }
            }
        })
    </script>
</body>

</html>